Water extracting device for paper machines



March 8, 1966 w, KNOWLES 3,239,410

WATER EXTRACTING DEVICE FOR PAPER MACHINES Filed May 24, 1963 1N VENTOR.7km dd 1 (mum/4n United States Patent 3,239,410 WATER EXTRACTING DEVICEFOR PAPER MACHINES Douglas W. Knowles, Erindale, Ontario, Canada,assignor, by mesne assignments, to Canadian General Electric Company,Limited, Toronto, Ontario, Canada Filed May 24, 1963, Ser. No. 283,101 5Claims. (Cl. 162-352) This invention relates to Fourdrinier paper makingmachines and more particularly to improved liquid drainage apparatus.

The forming of a pulp web in a Fourdrinier machine is made in such a waythat a mixture of water and fibre flows out of a head box to a movingendless wire screen, the water being then drained from the mixture as ittravels on the wire to a point where it is finally compacted by theapplication of high vacuum and the web is strong enough to be removedfrom the wire.

In this process it is essential that the stock be drained adequatelyprior to its final compaction, otherwise the best results in paperstrength and quality are not obtained because the fibres of the stocktend to lump together in a non-uniform paper formation. However, it hasbeen found that with adequate drainage a dilute stock is desirablebecause it gives a more uniform formation of the paper fibres withresultant increase in strength and quality of the paper but the use ofsuch stock accentuates the problem of such drainage and proposals havebeen made to increase the hydrostatic head on the wire during the earlypart of its travel.

To this end, high vacuum boxes have been employed but these have thedisadvantage that the drag imposed on the wire results in added wear andfurthermore sagging of the stock on the wire takes place, with resultantnon-uniformity of the thickness of the paper unless table rolls aresupplied underneath the wire to give the requisite support.Unfortunately, such table rolls themselves create a problem of throwbackof the liquid carried around in the rolls causing disruption of thepartially orientated fibres thus impairing the drainage and hence thequality of the finished paper. Furthermore, such high vacuum suctionarrangements are costly of construction because complicated andexpensive sealing mechanisms are required.

Alternatively, attempts have been made to employ low suction vacuumboxes operating directly under the Wire, but this again suffers in themain from the difficulty of providing a constant seal between the boxesand the wire.

The result of the difficulties experienced with high and low vacuumboxes has been a general reliance on free gravity drainage in commercialmachines in the early stage of travel of the stock on the wire, but itwill be appreciated that if such gravity drainage is just adequate witha particular dilution of stock the only method of achieving the sameadequacy if a more dilute stock is used with the intention of producinga higher quality of paper is to reduce the rate of movement of the wire.This curtailment of the speed of the wire means that the rate ofproduction is adversely affected. In the interests of flexibility andmaximum eificiency it would be desirable to introduce simple andinexpensive means which would augment the gravity drainage whennecessary.

To this end a member or deflector is positioned under the wire inclinedin a direction corresponding to the travel of the stock, the upper endof the deflector being substantially in a plane with the underside ofthe wire whereby hydrodynamic suction takes place in the zone subtendedby the wire and the member resulting in withdrawal of liquid from thestock in a flow downward over the upper surface of the deflector. Thenatural extent of the hydrodynamic suction zone is determined by the ingpositive means to energize extent to which turbulence can be delayed orlaminar flow preserved in the liquid flowing on this upper surface, theterm laminar flow designating regular and smooth steady motions which donot show the irregular fluctuations characteristic of the turbulentflows, the existence of which will depend on differences in the rate oftravel from the outside to the inside within the liquid flow.

The improvement of the invention consists in providthe static orboundary layer of the liquid adjacent to the upper surface of thedeflector to give it motion thus delaying separation of the fastermoving liquid further removed from the upper surface of the deflector.By this means the distance of laminar flow on the upper surface of thedeflector is extended and the zone of hydrodynamic suction of the stockon the wire is increased thereby augmenting the drainage.

It is then an object of this invention to provide apparatus whereby thelength of stock subjected to hydrodynamic drainage may be reduced whilegiving the required result of high strength and quality of the drainedweb, the apparatus being simple and inexpensive.

This and other objects, features and advantages of this invention willbecome apparent to one skilled in the art from the following descriptionof the embodiment illustrated in the accompanying drawings.

FIGURE 1 is an elevational diagrammatic view of a preferred embodimentof the invention showing parts in vertical section;

FIGURE 2 is an elevational diagrammatic view of another preferredembodiment of the invention with parts in vertical section.

As shown in the drawings:

In the embodiment shown in FIGURE 1 a travelling forming wire 10 carriesstock 11 thereon. A deflector 12 having its upper part inclined in adirection corresponding to the travel of the stock 11, supports the wire10, the lower part of the deflector 12 being carried by supports 13attached to a base 14. The length and relative position of the supports13 are adjustable so that the inclination of the deflector 12 inrelation to the wire 10 may be varied. The upper end of the deflector 12is substantially in a plane with the underside of the wire 10 and waterextracted from the stock 11 by hydrodynamic suction flows over the uppersurface of the deflector 12. At the lower end of the deflector 12 a roll15 is positioned so that its upper surface and the upper surface of thedeflector 12 form a substantial continuous surface, the aperture 16between the lower end of the deflector 12 and the surface of the roll 15being just large enough to ensure that there is no frictionalengagement. The roll 15 is supported through its axle 17 by means ofmembers 18 attached to the base 14; the length of these members 13, asalso their position on the base 14, can be varied to alter the positionof the roll 15 along with any alteration in the inclination of thedeflector 12 so that an upper part of the surface of roll 15 alwaysprovides a substantially continuous surface with the upper surface ofthe deflector 12. Drive means, not shown, are provided to rotate theroll 15 in a direction corresponding to the movement of the wire 10 andit is rotated at a velocity whereby it provides a downward and forwarddrag on the laminar fluid flow the upper surface of the deflector 12.

The speed of rotation of the roll 15 constitutes a control means forextending the natural hydrodynamic suction zone created between the wire10 and the deflector 12, the extent of this natural zone in crosssection being indicated by the curved line A. The extension of this zoneby means of rotation of the roll 15 can be best appreciated byconsidering the theory of fluid film, this being introduced for thepurpose of understanding and not by way of limitation. It is generallyrecognized that tionless flow of the fluid and ,the boundary layer in--creases the further the fluid travels along an inclined surface of thedeflector 12 and there comes a point when the diflerence in speed issuflicient to create turbulence and eventual separation of the films. Atthis point the pull of the fluid travelling along the inclined surfaceof the deflector 12 on the hydrodynamic suction zone will be disruptedand this is the reason for the limitation in the amount of dewatering ofthe stock 11 which takes places by gravity suction.

The rotation of the roll 15 exerts a downward and forward movement tothe. boundary layer of the liquid flowing along the upper'surface of thedeflector 12 and it follows from the above explanation that this willaid the persistence of laminar flow of the liquid if the boundary layerof the fluid film is effectively energised. In this way separation ofthe films will be delayed extending the zone of hydrodynamic suction toB and B etc., depending on the speed of rotation of the roll 15 and agreater length of the stock 11 on the wire will be subjected todewatering.

In operation the extent of the zone of the hydrodynamic suctionsubtended between t-he deflector 12 and the wire 10 will be determinedvisually and the position of the roll 15 adjusted until the uppersurface of the roll 15 enters the zone. The roll 15 will then be rotatedat the desired speed to energize the static boundary layer of theflowing liquid on the deflector 12 thus extending the hydrodynamicsuction zone and augmenting the dewatering of the stock 11; the extentof the suction zone may be increased by rotating the roll 15 at a higherspeed.

In the embodiment shown in FIGURE 2 the deflector 12 has apertures 19connecting the upper and lower surfaces which are inclined in a forwardand downward direction in relation to the movement of the wire 10. A

water supply 20 under pressure is directedagainst the under surface ofthe deflector .12 and this flow of water through the apertures 19 to theupper surface of the and the angle of the deflector 12 will be theFourdrinier type having a screen arranged to be driven in apredetermined direction, comp-rising: deflector deflector 12 provides apressure differential which ener- I gizes the static boundary layer,thus extending the zoneof suction and augmenting the dewatering of thestock 11.

It will be understood that modification and variation may be effectedwith-out departing from the scope of the novel concepts of the instantinvention.

What I claim is:

1. Dewatering apparatus for use with a machine of means for mountingbeneath the screen, to extend transversely in relation to saidpredetermined direction and having an upper surface and a lower surface,the upper edge of said upper surface. of the deflector means contactingthe under surface of the screen for. at least a portion of its length,said upper surface diverging downwardly from theflscreen in saidpredetermined direction to position the lower edge thereof from the;screen,

said deflector means including energizing .means having a surface movingin close proximity with said lower edge to energize liquid flowing; fromthe screen over the deflector means whereby the hydrodynamic suctioneffect between said deflector means andthe screen is improved.

2. A dewatering apparatus as claimed in claim 1 where-- in saidenergizing means comprises a roll positioned in close running relationto the lower edge of said deflector, and drive means to rotate saidroll.

3. Dewatering apparatus for userwith a machine of the Fourdrinier typehaving a screenarranged to be driven in a predetermined direction,comprising: deflector means for mounting beneathrthe screen; to extendtrans: versely in relation to said predetermined direction and having anupper surface and a lower surface, the upper edge ofsaid upper surfaceof the deflector means contacting the under surface of the screen for.at least a portion of its length, said upper-surface-diverging downwardly from the screen in said predetermined direction to position thelower 'edge thereoffrom the screen, a lower portion of the upper surfaceof said deflection means including the upper surfacev of'a roll inlcloseconformity with the upper portion of-the deflection means to-provide: asubstantially continuous'surface, and drive means for rotating the rollin:a direction corresponding with said predetermined screen directionwhereby'the rotation of 'said roll energizes liquid flowing from'thescreen over the deflection means, to improve the hydrodynamic suctionexerted on said screen.

4. Dewatering apparatus as claimed in claim, 3'includ-v ing adjustablemounting means for adjusting the mounting of said deflector and saidroll;relative to said screen.

5. Dewatering apparatus asclaimed in claim4 wherein said adjustablemounting means permits adjustment of said roll relative to the .upperportion of said deflector means.

References Cited by. the Examiner UNITED STATES PATENTS 2,170,109 8/1939Berry 2,694,345 11/1954 Hornbostel

1. DEWATERING APPARATUS FOR USE WITH A MACHINE OF THE FOURDRINIER TYPEHAVING A SCREEN ARRANGED TO BE DRIVEN IN A PREDETERMINED DIRECTION,COMPRISING: DEFLECTOR MEANS FOR MOUNTING BENEATH THE SCREEN, TO EXTENDTRANSVERSELY IN RELATION TO SAID PREDETERMINED DIRECTION AND HAVING ANUPPER SURFACE AND A LOWER SURFACE, THE UPPER EDGE OF SAID UPPER SURFACEOF THE DEFLECTOR MEANS CONTACTING THE UNDER SURFACE OF THE SCREEN FOR ATLEAST A PORTION OF ITS LENGTH, SAID UPPER SURFACE DIVERGING DOWNWARDLYFROM THE SCREEN IN SAID PREDETERMINED DIRECTION TO POSITION THE LOWEREDGE THEREOF FROMTHE SCREEN, SAID DEFLECTOR MEANS INCLUDING ENERGIZINGMEANS HAVING A SURFACE MOVING A CLOSE PROXIMITY WITH SAID LOWER EDGE TOENERGIZE LIQUID FLOWING FROM THE SCREEN OVER THE DEFLECTOR MEANS WHEREBYTHE HYDRODYNAMIC SUCTION EFFECT BETWEEN SAID DEFLECTOR MEANS AND THESCREEN IS IMPROVED.